An inflatable packer is a normally retracted wellbore sealing device that is expanded into sealing contact with a well conduit wall by pumping fluid under pressure into the interior of the packing unit. When inflation pressure is relieved, the packer unit will inherently retract toward its original diameter so that it can be removed from the well. The packer unit typically includes an inner elastomer bladder that is covered externally by a reinforcement that prevents extrusion of the bladder under pressure and which is the principal load bearing member when the packer is set.
A reinforcement that has been widely used is an assembly of longitudinal, circumferentially overlapped metal slats whose opposite end portions, together with opposite end portions of the bladder, are anchored to annular upper and lower fittings on the packer mandrel. The slats are long and rectangular in shape and have sufficient overlap when the packer unit is retracted that they still completely cover the bladder when the unit is fully expanded to provide a barrier against extrusion of the bladder.
Since the metal slat assembly which forms the reinforcement is the principal load bearing member as well as the extrusion barrier for the inner elastomer bladder, the design of this type packer is directly related to how the slats are to be packaged. The three principal parameters in the design are 1) total cross-section area of slat material 2) extrusion barrier requirement, and 3) slat deployment as the packer unit expands. The first parameter is independent of slat geometry in terms of width and number. However in connection with the second parameter the applicants have found that it is preferable to have numerous thin slats rather than a few thick slats, with the ultimate goal being to have the maximum slat surface area that can be packaged on the end fittings. The third parameter mainly governs the width of each slat. Here it is preferable to have a wider slat which will deploy better during inflation due to increased lateral stiffness. For example a 1 inch wide slat is eight (8) times stiffer than a 1/2 inch wide slat.
Using the expansion ratio for the packer unit (i.e. the ratio of its expanded and retracted outer diameters) and the differential pressure requirements for a particular type of well service operation, the minimum slat cross-sectional area and surface area can be determined. From these values, the slat width and thickness can also be determined. From the standpoint of slat deployment, it would appear advantageous to have extremely wide but thin slats. However the strain in the slat where it anchors to the end fitting is directly proportional to width. Thus the maximum strain that a slat material can withstand is the principal determining factor of slat width.
With the foregoing factors in view, it is an object of the present invention to provide a new and improved reinforcing slat design for an inflatable well packer which is dimensioned to provide optimum characteristics for load bearing as well as extrusion barrier and deployment.
Another object of the present invention is to provide a new and improved reinforcing slat assembly for use in an inflatable packer and where each slat has one cross-section area at its end portions which will bear the required loads at the end fittings, and another larger cross-sectional area throughout the balance of its length which provides the required extrusion barrier and deployment characteristics.
Still another object of the present invention is to provide a new and improved reinforcing assembly for an inflatable packer where each slat has uniform width end portions and variable width intermediate portions to control packer shape and deployment during inflation.